1. Field of the Invention
This invention relates to the treatment of pain in humans using electrical pulses.
2. Description of the Related Art
A background of knowledge is required to adequately understand occipital neuromodulation. The following is an attempt to summarize this knowledge.
Pain is a form of sensory input that is conveyed to the brain via our nervous system. Within the brain, pain is processed within discrete processing centers. These discrete processing centers are being discovered through the use of functional MRI and PET scans which show the metabolic activity within the brain. One can see how active a given area of the brain is by looking at its metabolic activity. Areas that are quiescent have lower metabolic activity compared with those that are active. With the use of such imaging modalities, a map is made of the metabolic activity within the brain. That baseline map of activity can then be compared to that seen when various types of sensory input are applied to a test subject. It is therefore possible to demonstrate changes within the brain caused by specific activities or forms of sensory stimulation. Furthermore one can observe changes in the brain when those specific activities or forms of stimulation are withdrawn.
The nervous system involves both electrical and chemical activity. There is both electrical activity involving the transmission of electrical signals, as well as the balance of chemical agents known collectively as neurotransmitters. There is a direct relationship between neurotransmitters and the transmission of electrical activity. Certain neurotransmitters increase or potentiate electrical activity. Others decrease or suppress electrical activity. For the purpose of this invention, neuromodulation is the act of using electrical signals from a peripheral nerve outside the brain to alter the balance of neurotransmitters within the brain.
The processing of pain information in discrete areas of the brain leads to alterations in other regions of the brain which makes this information manifest in what we consider our perception. The communication between the processing centers and these other regions occurs both on an electrical level and on a chemical level (nerves and neurotransmitters). As an illustration, patients with intractable depression respond to electroconvulsive therapy. By repeatedly inducing a massive electrical charge over the brain, the electrical system is reset and the depression alleviated via a change in the balance of neurotransmitters.
Yet another example is vision. To illustrate, we can easily read misspelled words as long as the first and last letters in each word are correct. Recently, a popular e-mail has circulated demonstrating this phenomenon of which many people have already seen. We can read such misspelled words since the processing centers for vision within our brains corrects the misspelled words.
The sensation of pain has been studied in this fashion. There is a growing body of literature surrounding this idea of the true nature of pain. A recent study was published by Dr. Marwan Balicki in The Journal of Neuroscience, Feb. 6, 2008. The authors of the study used functional MRI scans on both people with chronic pain and without and mapped out the differences in metabolic activity within the brain. What they found was that areas of the brain that were normally quiet in people when concentrating on a television screen were still active in the patients with chronic pain. These areas involved the processing of pain. When people without pain watched the television, these areas of the brain were metabolically quiet (like an engine in neutral). When patients with chronic pain watched the television, these areas of the brain were abnormally metabolically active (like an engine that was running at high RPM's).
There has also been recent research regarding the use of mirrors to relieve phantom limb pain. Apparently, when an amputee holds a mirror to create the visual illusion of having two normal limbs and moves the remaining limb, the brain processes the information in such a way so as to alleviate the pain coming from the missing limb. Through the use of creating an illusion of an intact limb, the processing of pain within the brain normalizes. A recent study in the New England Journal of Medicine elucidates this further: Chan B L, Witt R, Charrow A P, Magee A, Howard R, Pasquina P F, Heilman K M, Tsao J W Mirror Therapy for Phantom Limb Pain, New England Journal of Medicine, Nov. 22, 2007.
Functional MRI studies with patients with fibromyalgia also show abnormalities compared with normal controls. In a study performed by Williams and Gracely in Arthritis Research & Therapy 2006 using Functional MRI, the authors clearly showed abnormally increased metabolic activity in the processing centers for pain in patients with fibromyalgia. Fibromyalgia patients feel pain initially in one section of their bodies but over the years, the sensation of pain spreads across their bodies. Diagnostic tests of these painful areas such as X-rays and conventional MRI's show no pathology in the muscles or joints, but the pain persists. The term fibromyalgia is now considered as a misnomer since this pain syndrome is a central pain syndrome within the brain and has nothing to do with the fibrous or muscular tissue denoted by the meaning of the word “fibromyalgia”. Occipital neuromodulation has been used to successfully treat the pain of fibromyalgia.
There is a study using stimulation of occipital nerves which demonstrated alterations in metabolic activity within the brain which was different depending on whether the device was active or not. The Neurosurgery and Neuroscience Divisions at the National Hospital for Neurology and Neurosurgery in London in conjunction with the Department of Neurosurgery in Dallas performed PET scan studies in 2004 on patients with traditional occipital stimulators. Matharu et al., infra. The studies found that occipital stimulation alters metabolic activity in the anterior cingulate cortex, left pulvinar, and dorsal rostral pons. These areas are considered to be the processing areas for pain.
The current belief is that chronic pain results in an electrical and chemical restructuring within the brain to promote the continued perception of pain. Even when the original anatomical cause for the pain has healed or has been surgically corrected, the pain may initially improve, but then returns. In many cases, the pain is unaltered despite the correction of the anatomical cause. In the field of pain management, this phenomenon is known as the “centralization of pain.” The pain persists due to alterations in the processing centers for pain.
With this background, we will proceed to the technical aspects of occipital neuromodulation. Occipital neuromodulation is a significant improvement of the technology of spinal cord stimulation that has been in use since 1967. The concept behind spinal cord stimulation was that by imposing an external electrical field over the spinal cord, the transmission of pain signals to the brain could be interrupted, and thus relieve pain. Over the years, the technology became more advanced and the equipment became smaller. Approximately 17 years ago, it became possible to use the same equipment to stimulate small peripheral nerves and thus the discipline of peripheral nerve stimulation came into vogue. Approximately 16 years ago, physicians started using this equipment to stimulate the occipital nerves which are sensory nerves that run up the back of the head (the occipital region) to relieve the pain of migraines. For a number of years prior, it had been demonstrated that blocking the occipital nerves with local anesthesia could stop a migraine and reduce the frequency of its reoccurrence. This showed a link between the occipital nerves and migraines. So with that link in mind, physicians began using occipital stimulators to relieve migraines.
But it is much more complicated than that. In 2004 there was a study published in Brain, Volume 127, No. 1 pp. 220-230 by Matharu et. al. In the study there were eight patients who had peripheral occipital nerve stimulators for chronic migraines. Each patient had two PET scans performed to map out the metabolic activity in the brain. One scan was performed with the device off, the second with the device on. There was a consistent pattern in changes in the metabolic activity within the pain processing centers in each of the eight patients. Therefore, the stimulation of a peripheral nerve was shown to cause changes within the brain itself. By stimulating a peripheral nerve electrically, there was a change in activity reflected in the pain processing areas within the brain.
One non-drug method that has been tried is disclosed in U.S. Pat. App. Pub. No. 2008/0045776 A1, by Fischell et al, published on Feb. 21, 2008, and which is not admitted to being prior art by its mention in this Background section. Fischell discloses a method and apparatus of treating headaches using a head-mounted magnetic depolarizer to generate a high intensity magnetic field around the user's head or neck. The depolarizer can be placed over the occipital region to generate a magnetic field one centimeter below the skin with a force between 0.1 and 5 Tesla. The purpose is to depolarize the neurons of the trigeminal nerve for terminating a migraine and other types of headaches after onset of aura but before the full migraine occurs. Although the apparatus is non-invasive, it is not suited for wearing on the body for more than a short period of time. In addition, it only treats headaches, and not other painful neurological ailments.
An apparatus that has been tried is disclosed in U.S. Pat. App. Pub. No. 2006/0074450 A1, by Boveja et al., published on Apr. 6, 2006, and which is not admitted to being prior art by its mention in this Background section. Boveja discloses a system for stimulating nerves or muscles to treat a variety of conditions, including occipital neuralgia and transformed migraine. However, the electrical signals used reveal that the system “stimulates” nerves in the sense that pain signals are overpowered and the subject will feel a tingling sensation. Although feeling the tingling is probably better than feeling pain, it would be advantageous if the system relieved pain without imposing a tingling sensation on the subject.
A method that has been tried is disclosed in “Central Neuromodulation in Chronic Migraine Patients With SubOccipital Stimulators: A PET Study,” Brain, Vol. 127, No. 1, Nov. 7, 2003, pp. 220-230, by Matharu et al., which is not admitted to being prior art by its mention in this Background Section. Matharu taught the use of sub-occipital simulators for the treatment of migraine only. The electrical signals had a pulse width between 90 and 180 msec, frequency between 60 and 130 Hz, and amplitude between 1.5 and 10.5 V. The electrodes were positioned superficial to the cervical muscular fascia and transverse to the greater occipital nerve trunk at the level of the first cervical vertebrae (an anatomically different location than that used in occipital neuromodulation). One of the findings stimulator-induced paresthesia relieved pain.
Another method is disclosed in “Neuromodulation of the Occipital Nerve in Pain Management,” Techniques in Regional Anesthesia and Pain Management, Vol. 10, No. 1, January 2006, pp. 10, 12-15, by Vallejo et al., and which is not admitted to being prior art by its mention in this Background section. This paper discloses a procedure for electrically stimulating the occipital nerve with electrodes coupled with an external programmable generator. The process treats occipital neuralgia. The paper does not define “neuromodulation” or provide any specific information about the composition of the electrical signal. However, since the process is performed with the patient awake and includes searching the patient's reported paresthesia (feeling the tingling sensation) in the areas of the pain (Id. at p. 14), one may conclude that the process stimulates the nerve well beyond the threshold to evoke the sensation of paresthesia.
Another system and method that has been tried is disclosed in U.S. Pat. App. Pub. No. 2006/0047325, by Thimineur et al, published on Mar. 2, 2006. This patent application is not admitted to being prior art by its mention in this Background section. Thimineur claims his device and process can block the perception of pain throughout the body, improve motor coordination, treat mental retardation, autism, Alzheimer's dementia, Parkinson's, pathological gambling, schizophrenia, postoperative ileus, Crohn's disease, rheumatoid arthritis, systemic lupus erythematosus, asthma, pituitary tumors, endometriosis, infertility, atherosclerotic cardiac disease, valvular heart disease, heart attacks, hypercholesterolemia, hypertension, diabetes, etc. His electrical stimulation parameters are a pulse width between 5 and 200 msec, frequency between 3 and 50 Hz, and amplitude between 2 and 100 mA. He claims to block pain by stimulating the spinal cord at the level of C2 (the second cervical vertebrae—an entirely different anatomical location from that of the present invention). A single pair of leads is used which is different than the present invention. Thimineur sets the device to cycle on and off (e.g. one minute on, ten minutes off).
Also, in the Thimineur method, the right and left leads are programmed identically with the same amplitudes. Therefore the power output from the right lead is always set the same as the left. It has been found however, that such parameters inevitably result in an imbalance of energy actually being delivered to the targeted nerves. The distance of each individual lead to its targeted nerve is different from the right side of the head to left side of the head. The scar tissue that develops from surgery and insulates each lead is also different from right to left. The scar tissue continues to grow over time and thus continues to create differences as well. The success rate of Thimineur's method has been reported to be 66%.